(1) Field of the Invention
The present invention relates to a material and apparatus for selectively removing dental caries without damaging sound dentine.
(2) Description of Related Art
Dental caries occur and progress by the following mechanism. Dentine consisting of inorganic and organic components is bated by acids produced by bacteria and thus softens. Subsequently, the remaining organic components are decomposed by bacteria, creating voids.
Dental caries would recur unless portions softened and invaded with bacteria are removed. Thus, caries must be fully removed.
Heretofore, dental caries have been cured by grinding the caries including sound dentine and forming a box-like portion to prevent the filler from coming off. In recent years, bonding resinous materials have been developed. Therefore, the filler adheres strongly to dentine. When caries are cured, it is not necessary to grind sound dental. Consequently, it has become important that caries be fully removed and sound dentine be left as much as possible.
Today, one main means for knowing the range of caries is to detect the hardness of the caries. Another main means is to know native coloration of caries. A further main means is to color the caries with a caries-detecting liquid. In particular, only the caries are dyed red. Currently, this is the most reliable method of knowing the range of caries. Removal of caries is started with removing softened caries portions sufficiently. Native colored portions due to caries or portions dyed with a caries-detecting liquid are removed with ultimate care such that sound dentine is not damaged. A round steel bar attached to a micromotor that is a rotating grounding tool has been chiefly used to remove caries.
Dental caries are so softened that the hardness on the surface-layer side cannot be measured with a Vickers hardness tester (JIS Z 1051). The hardness suddenly increases at the boundary with sound dentine and exhibits values of approximately 10 to 30 Hv. On the other hand, sound dentine shows a hardness of approximately 60 to 80 Hv.
Dental caries are removed within a narrow region of a mouth. The practitioner cannot directly view the caries, depending on the position. In this case, he or she can view the caries only with a mirror. Therefore, depending on the skill of the practitioner, the caries might be fail to be removed, in which case the caries would recur. Also, sound dentine might be excessively ground. Furthermore, long treating time and much labor are necessary even for experienced practitioner. Today, there is a demand for a method of removing only caries in a short time without depending on the skill of the practitioner.
Where grinding is done with an air turbine or a micro-motor that is one of rotating grinding tools, both caries and sound dentine are ground. Therefore, only the feasible method is to select and grind only caries, depending on the skill of the practitioner. In recent years, an air-blasting apparatus using alumina grinding material has begun to be used in clinical applications. With this apparatus, sound dentine is more easily ground than caries. It is considered that it is difficult to use this apparatus to remove caries. Therefore, any method other than the method consisting of removing only caries by a practitioner with utmost care has not been developed.
We have found that only caries can be removed without grinding sound dentine by using grinding granules as material ejected from an air-blasting apparatus. The hardness of the grinding granules is not so high that sound dentine is not ground. We have proposed a caries-removing material consisting of grinding granules having a hardness equal to or less than the hardness of sound dentine, in Japanese Patent Laid-Open No. 276292/1997 (patent application Ser. No. 343730/1998).
To assure that dental caries formed in narrow regions are removed, it is desired to eject air from an ejection nozzle having a diameter of less than 1.0 mm. We have discovered that commercially available caries-removing materials such as Tyler mesh #60 are obtained by pulverizing stones of seeds of peach or apricot. If such a material is left within the mouth, little feeling of wrongness is imparted to the patient. If the patient swallows a small amount of the material, no problems take place. Furthermore, caries can be ground well with this material. However, we have discovered that the nozzle is easily clogged with this material. The stones of peach, or Tyler #60, were pulverized and granulated with micromesh. Those of the obtained granules which lie in a narrow range were used. Even in this case, the gums feel a pain, though the nozzle does not clog up.